It is common in modern optical networks for the ingress of the transport network to use an optical transponder as a termination point for converting a ‘gray’ low cost optical signal from a customer's optical interface to a ‘colored’ optical signal on a service provider's network element. The ‘colored’ optical signal, or Wavelength Division Multiplex (WDM) signal, is typically enhanced, or ‘digitally wrapped’ with Optical Transport Network (OTN) overhead to provide service transparency, performance management capabilities and Forward Error Correction (FEC) coding for increased optical reach across the transport network. The WDM signal may then be transmitted across one or more optical links and through numerous intermediate devices before reaching the egress point of the transport network. At the egress point the WDM signal is terminated optically, the OTN overhead is removed and processed, and the remaining signal is converted back to a ‘gray’ low cost optical signal for transmission to the customer.
The transponder serves as the demarcation point between the operation, control and ownership of facilities of the service provider's network, hereafter referred to as SP, and the customer premise equipment. Examples of customer premise equipment may include a server, router or switch located at the campus of a business or it could be a WDM Terminal or Reconfiguration Optical Add Drop Multiplexer (ROADM) edge node from an SP in a different administrative domain.
Additionally, it is often also desirable to provide various forms of redundancy for equipment and/or facilities within the SP's network. Redundancy enables the signal transport service provided to the customer by the SP to be maintained in the event of failures of either equipment or transmission spans. Various forms of equipment and facility protection are well known to those skilled in the art, and may be utilized singly or in combinations, or indeed not employed at all, in support of a given service instance.
FIG. 1 shows an example network wherein the operation, control and ownership domain of the SP is depicted in the shaded portion of the figure while the operation, control and ownership domain of the customer is depicted in the un-shaded portion of the figure. Since the service edge network elements of the SP perform optical-to-electrical-to-optical (OEO) conversion on each incoming and outgoing signal to and from its network, it is able to isolate and verify the quality of the received customer optical signals as they enter the SP's network and it is able to isolate and verify the quality of the optical signals within the SP's network. If there is a problem, the SP is able to identify the source of the problem as either within or outside of its own network. The customer optical interfaces are here each connected to 2 different transponders (labeled TXP) at the corresponding edges of the SP's network. This allows the SP to provide protection for the signal conveyed between the customer optical interfaces by selectively controlling which one of the two routes within the SP's network is made active. In this figure, if any equipment or segment of the upper route fails, the lower route may be used as an alternate in order to maintain service, and vice versa.
Routing high speed optical signals across a transport network is very complicated. The signals may traverse long distances over multiple spans and through numerous nodes each of which may contain various components that impact the end to end quality of the optical signal. Example intermediate devices may include amplifiers (Erbium Doped Fiber Amplifier (EDFA) and Raman) and ROADMs of different types; all of which have the potential to impair the optical signal.
Many of the intermediate devices in current optical networks require time to stabilize their operation when the optical signals passing through them change in some appreciable manner. For example, many optical amplifiers perform operations such as channel power level balancing, gain flattening, and/or constant gain or constant power regulation of the composite optical signal being amplified, and some of these operations take several seconds or even minutes to compensate for changes in the optical signal characteristics, such as when an optical channel signal is added to or removed from the composite optical signal passing through the amplifier.
By way of example, referring again to FIG. 1, should the signal from a transponder on the upper route fail, the composite optical signal within the SP's network between the transponders at either end along that route will experience a change in characteristics, due to the loss of the optical signal from the failed transponder. If the lower route, acting as an alternate for the upper, is not already conveying an optical signal between the transponders at either end, the composite optical signal along that route may also experience a change when the SP's network activates an optical signal on the lower route providing protection for the customer's service.
Due to the potential adverse impacts on the composite signals and the time interval required to stabilize the elements along the route in the event of such changes, modern optical networks often provide such redundancy using a technique referred to as “hot standby”. In a hot standby configuration, both the normally utilized (“normally working”) and the alternate (or “redundant”, “backup”, protection” or “hot-standby”) routes convey optical signals between the ends of the two routes. Herein, the “hot standby” phraseology refers to the fact that the alternate route conveys an optical signal whose optical properties approximate that of the signal used when conveying the customer's signal along that route. In the FIG. 1 example wherein the lower route acts as a hot standby alternate for the upper, the selection of the route to be used for transporting the customer's signal between the customer optical interfaces would include controlling the selection of the spans between the customer optical interfaces and the transponders adjacent to them. By placing the customers information onto one or the other of the SP's optical routes, the SP is able to choose which of the routes is used to convey the information, and therefore to provide alternate routing in the event of a failure affecting one of the routes.
FIG. 2 depicts another prior art example of protected services. In this example, the SP provides two independent network routes, and protection is controlled by the customer. Such a configuration is sometimes used, by way of non-exhaustive example, to connect two IP routers. In such a configuration, the SP provides two routes, each of which is unprotected from their point of view. The customer is then free to utilize both of these routes, providing double the information transfer capacity when both routes are operable, and the ability to protect one half the prior total capacity by using the non-failed route when one route fails.
FIG. 3 depicts another prior art example of protected services. In this example, the customer optical interfaces are transported transparently through the SP's network utilizing support for alien wavelengths provided by the SP's network. As in FIG. 2, protection is controlled by the customer, and the SP view's each of the routes as independent and unprotected.
Co-pending application Ser. No. 13/490,314, titled “Remote Optical Demarcation Point”, filed Jun. 6, 2012, hereby included in its entirety by reference, has disclosed apparatus, methods and systems which allow placing WDM transceivers at a customer site without breaking the traditional model of independent control currently employed by the SP. That invention also allows the example depicted in FIG. 2 to be changed into a configuration similar to that depicted in FIG. 3, with the difference that the customer optical interfaces become the demarcation points of the SP's network, and connect, in turn, to further customer equipment not shown in FIG. 3.
While the aforementioned co-pending application enables protected services to be provided within such further customer equipment, it does not address the means by which the SP may provide equipment and/or route protection in a scenario similar to that depicted in FIG. 1, with the difference that the customer optical interfaces have become remote optical demarcation points of the SP's network through the use of said co-pending invention.
Since a significant number of customer services similar to those depicted in FIG. 1 are offered by SP's, it is therefore desirable to provide apparatus, methods and systems which enable equipment and/or route protection to be realized in conjunction with the benefits of the remote optical demarcation point apparatus as disclosed by said co-pending non-provisional application. It is further desirable that said apparatus, methods and systems be compliant to relevant standards and recommendations, such as, but not limited to, ITU-T Recommendation G.698.2. It is still further desirable that said apparatus, methods and systems enable the simultaneous support of both equipment and route protection.